I m using tectia MFT Event 6.1 to upload public key.I m placing my public and private keys under C:\Documents and Settings\s-SshMft\Application Data\SSH\UserKeys.But keys are not appearing in key and certificate list.So,I haven't able to upload OPEN SSH public key through MFT Event.
So, I m trying to convert public and private keys compatible with tectia and upload it. I m able to convert public key and but not able to convert private key.

Is the private key passphrase protected? I believe the --import-private-key only works for unencrypted private keys.

Can you edit your answer to explain what is it that you're trying to do by converting the key? If you're using a recent enough (6.0 and newer) version of Tectia, both client and server allow the use of openssh keys without the need to convert them.